Why with decreasing grain size there is decrease in impact transition temperature?

Expert Solution

Question: Why with decreasing grain size, there is decrease in impact transition temperature?

Answer: The basic fundamental theory is - to improve the mechanical properties (yield strength) of any steel, it is necessary to heat the metal for a specified temperature. This is called heat treatment. During this heat treatment process, the grains get influenced for their sizes. So that, the mechanical properties (yield strength) of the steel will improve.

Reasons:

In transition temperature the Mechanical properties like yield strength & fracture strength will increase, if the grain size decreased. The Hall-Petch relation proves this statement.
The decrease in grain size tends to decrease in transition temperature – the reason is ‘fracture stress should be proportional to the ratio of surface energy'.
Grain size directly proportional to the yield strength, because of their movements in the grain boundary.
Grain refinement will improve the strength and lower the ductile-brittle transition of steel.

Thus the decrease in grain size causes to decrease in transition temperature.

samet mamat answered 2 years ago

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